Control of Microbial GrowthControl of Microbial Growth(Sterilization and Disinfection)(Sterilization and Disinfection)

Control of Microbial GrowthControl of Microbial Growth

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Microbial Control Microbial Control

Can inhibit growth of many microorganisms by washing and scrubbing with soaps and detergents.

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SterilizationSterilizationProcess of removing

or killing all microorganisms and viruses on or in a product.

– Ensures complete destruction of all microorganisms, including cells, spores, and viruses.

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Examples of SterilizationExamples of Sterilization

Dry heatAutoclavingGasVarious chemicalsCertain types of

radiation

Autoclave. www.lifelinemedical.net

Dry Heat Sterilization. www.kabdental.com

DisinfectionDisinfection Process that reduces # of

potential disease-causing bacteria and viruses on a material until they no longer present a hazard.

Terms decontamination and sanitation mean the same thing generally.

Disinfectant– A chemical used to disinfect

inanimate objects.

Example of Disinfection - Example of Disinfection - PasteurizationPasteurization

Method of disinfecting liquids.

Heat liquids to a certain temperature.

Does not totally destroy pathogens. Pasteurization Equipment.

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DecontaminationDecontamination

Inactivation or removal of both microbial toxins and the living microbial pathogens.

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AntisepticAntiseptic

Solutions used to disinfect skin and other living tissues.

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SanitationSanitation

Reduction of microbial populations to levels considered safe by public health standards. www.zerrenterprises.com

Microbicidal AgentsMicrobicidal Agents

The suffix –cide or –cidal refers to “killing.”

– Ex. Microbicidal agents (microbicides)

– Ex. Bactericidal agents

– Ex. Sporicidal agents

– Ex. Viricidal agents

Microbistatic AgentsMicrobistatic Agents

Microbistatic Agent Drug or chemical that inhibits the growth and reproduction

of microorganisms.

Bacteriostatic Agent One that specifically inhibits the metabolism and

reproduction of bacteria.

Microbistatic technique examples Ex. Lyophilization (freeze-drying) Ex. Rapid freezing (using liquid nitrogen)

Some Useful TermsSome Useful Terms Sepsis

Presence of pathogens in blood or tissues.

Asepsis Absence of pathogens. Ex. Hand washing; use of sterile gloves,

masks, gowns; sterilization of surgical equipment; use of disinfectants.

Antisepsis Prevention of infection.

Antiseptic technique Developed by Joseph Lister (1867). Use of antiseptics.

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Sterile TechniqueSterile Technique

Practice of excluding all microorganisms from a particular area, so that the area will be sterile.

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Controlling Microbial Growth Controlling Microbial Growth Using Physical MethodsUsing Physical Methods

Methods used to destroy or inhibit microbial growth may be physical or chemical.

Examples:HeatCombination of heat and pressureDesiccationRadiationSonic disruptionFiltration

HeatHeatPractical, efficient, and inexpensive method of

sterilization.

2 factors that influence effectiveness of heat for sterilization: temperature and time

– Thermal Death Point (TDP) Lowest temperature that will kill all organisms in a

standardized pure culture within a specified period.– Thermal Death Time (TDT)

Length of time necessary to sterilize a pure culture at a specified temperature.

Dry HeatDry Heat Heating materials in absence

of moisture.

Must be baked at 160º to 165ºC for 2 hours or at 170º to 180ºC for 1 hour.

Other methods include incineration and flaming surface of metal materials like forceps and loops.

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Moist HeatMoist Heat Boiling or steaming.

Most pathogens destroyed after 30 minutes of boiling.

Boiling not always effective against some endospores and viruses.

Boiling not an option for thermophiles.

Boiling. ttt.astro.su.se

Steamer. www.appliancist.com

Autoclaving Autoclaving Large metal pressure

cooker that uses steam under pressure to completely destroy all microorganisms.

Increased pressure raises the temperature of boiling water (i.e. above 100ºC) producing steam.

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Home CanningHome Canning Use of a pressure

cooker.

If foods canned without pressure some bacterial endospores may survive.

i.e. Clostridium botulinum

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Bulging lid – botulism. calorielab.com

Disinfecting TechniquesDisinfecting Techniques

For clothing, bedding, and dishes

Use hot water with soap or detergent

Agitate solution around items

Combination of heat, mechanical action, and chemical inhibition kills most microbes. Washing Machine.

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Cold Cold Metabolic activities slowed.

Most microbes not killed, but growth inhibited.

Slow freezing not a good way to preserve bacteriological or biologic specimen.

Rapid freezing (liquid nitrogen) good for this.

Why should you not refreeze foods?

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Slow Freezing.

Rapid Freezing – liquid nitrogen. encarta.msn.com

DesiccationDesiccation

Process of drying materials.

Many microbes can remain viable despite absence of nutrients and moisture.

Ex. Lyophilization (freeze-drying)

Dried blood, fecal material, and dust may still contain viable microbes.

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Radiation Radiation Ultraviolet (UV) light sometimes used to

prevent or decrease microbial growth.X-rays and gamma and beta rays may be

used to destroy or prevent microbial growth.

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Ultrasonic WavesUltrasonic Waves Often used to sterilize and clean delicate equipment.

Consists of tanks filled with liquid solvent (usually water).

Short sound waves are passed through liquid.

Sound waves dislodge organic debris.

Materials must then be washed and sterilized by another method.

Filtration Filtration Filters of various pore sizes are

used to filter or separate larger cells, larger viruses, bacteria, and other microbes from gases or liquids in which they are suspended.

Paper masks used to prevent the outward and inward movement of microbes.

wps.prenhall.com

health.howstuffworks.com

Gaseous AtmosphereGaseous Atmosphere

Altering atmosphere of microbes to inhibit growth.

Hyperbaric Chamber. www.perlhealth.com

Gas gangrene – caused by Clostridium spp. www.humanillnesses.com

Chemical Agents Used to Inhibit Chemical Agents Used to Inhibit Microbial GrowthMicrobial Growth

Temporarily or permanently.

Different disinfectants have different properties.

Disinfectants should be chosen based on their efficiency and effectiveness for a particular situation.

What Are Some Things to What Are Some Things to Consider When Choosing a Consider When Choosing a

Chemical Disinfectant?Chemical Disinfectant?

What makes an Ideal Chemical What makes an Ideal Chemical Antimicrobial Agent?Antimicrobial Agent?

How Do Disinfectants Kill How Do Disinfectants Kill Microorganisms?Microorganisms?

Some target and destroy cell membranes. Ex. Surface-active soaps and detergents; alcohols

Some destroy enzymes and structural proteins. Ex. Formaldehyde and ethylene oxide

Some attack cell walls or nucleic acids.

AntisepticsAntiseptics

Can be used safely on human skin.

Reduces # of organisms on the surface.

Does not penetrate pores or hair follicles.

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Preventing Growth of Pathogens Preventing Growth of Pathogens in Our Kitchensin Our Kitchens

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The Antibiotic Controversy The Antibiotic Controversy

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The EndThe End